94 electrical systems troubleshooting
Direct Alternating
Current (mA) Current (mA)
Effect Male Female Male Female
Slight sensation 1 0.6 0.4 0.3
Perception threshold 5.2 3.5 1.1 0.7
Shock, not painful, no 9 6 1.8 1.2
loss of muscular control
Shock, painful, still no loss 62 41 9 6
of muscular control
Shock, painful, “let go” 76 51 16 10.5
threshold
Shock, painful and severe, 90 60 23 15
uncontrolled muscular
contraction, severe
breathing difficulty
Shock, possible ventricular 500 500 100 100
defibrillation following
3 seconds of exposureEffects of Electrical ShocksTABLE
10-1WHY IS RESIDUAL CURRENT LEAKAGE SO DANGEROUS?Residual current leakage into the water surrounding boats has risen to the top of the safety hazard
list in recent years because we now have indisputable proof that it has caused deaths in freshwater
lakes and rivers. The concern is not so great in salt water, because salt water is a good conductor of
electricity, and any leakage current is rapidly dissipated to earth, either on the dock or the bottom.
Fresh water, however, is a rather poor conductor of electricity. As current leaks from the bottom of
a boat, a voltage gradient tends to stratify near the surface of the water, migrating sideways around
the boat and seeking a path to earth on the shore. Because the human body is composed of a very
high percentage of salt water, a swimmer who enters this voltage gradient and aligns his or her body
with the gradient becomes a far more efficient current path than the water itself. Once exposed to
this current, a fatal heart muscle seizure may occur, and the swimmer is electrocuted.
How much residual current is potentially lethal? I use 30 mA as my baseline, simply because that
is the established standard everywhere in the world except North America. The 30 mA figure is less
than the AC figures given for ventricular defibrillation in Table 10-1, but it has been established almost
globally as a reasonable compromise between protection devices tripping constantly and extreme
pain for humans. Anything above that limit is, as far as I’m concerned, simply too great a risk to take.